Light pulse storage in Pr:YSO crystal based on the revival of silenced echo protocol.

We report on the light pulse storage in Pr3+:Y2SiO5 crystal based on the revival of silenced echo protocol, which has the advantage of being immune from the spontaneous emission noise. We optimized the echo retrieval efficiency of the light pulse by employing complex hyperbolic secant rephasing pulses and by finely tuning the optical depth in the inhomogeneous broadening of the crystal. An echo retrieval efficiency of 24.4% was demonstrated, and an optical coherence time of 34.6 µs was extracted from the measured decay dynamics of the echo retrieval efficiency at a cryogenic temperature of 3.4 K. These results could be useful for potential applications in quantum memory and related applications.

Evidence of 3D Topological-Domain Dynamics in KTN:Li Polarization-Supercrystal Formation.

We experimentally and theoretically investigate thermal domain evolution in near-transition KTN:Li. Results allow us to establish how polarization supercrystals form, a hidden 3D topological phase composed of hypervortex defects. These are the result of six converging polarization vortices, each associated to one orientation of the 3D broken inversion symmetry. We also identify rescaling soliton lattices and domain patterns that replicate on different scales. Findings shed light on volume domain self-organization into closed-flux patterns and open up new scenarios for topologically protected noise-resistant ferroelectric memory bits.

Ghost images with controllable visibility and spatial resolution.

We designed a kind of speckle field with controllable visibility and speckle grain size through a modified Gerchberg-Saxton algorithm based on Fresnel diffraction. Ghost images with independently controllable visibility and spatial resolution were demonstrated based on the designed speckle fields, which could be of much higher visibility and spatial resolution than those with pseudothermal light. In addition, speckle fields capable of reconstructing ghost images simultaneously on multiple different planes were customized. These results could be of potential applications on optical encryption and optical tomography.

Electrically tuned coupling of lithium niobate microresonators.

Microresonators coupled with integrated waveguides operate stably but usually lack tunability for an optimal coupling state. In this Letter, we demonstrate a racetrack resonator with an electrically modulated coupling on an X-cut lithium niobate (LN) platform by introducing a Mach-Zehnder interferometer (MZI) with two balanced directional couplers (DCs) to realize light exchange. This device provides a wide-range coupling regulation, from under-coupling and critical coupling to deep over-coupling. Importantly, it has a fixed resonance frequency when the DC splitting ratio is 3 dB. The measured optical responses of the resonator exhibit a high extinction ratio, exceeding 23 dB, and an effective half-wave voltage length Vπ·L of 0.77 V·cm, suitable for CMOS compatibility. Microresonators with tunable coupling and a stable resonance frequency are expected to find application in nonlinear optical devices on LN-integrated optical platforms.

Second-harmonic and cascaded third-harmonic generation in generalized quasiperiodic poled lithium niobate waveguides.

Lithium niobate (LN) thin film has recently emerged as an important platform for nonlinear optical investigations for its large χ(2) nonlinear coefficients and ability of light localization. In this Letter, we report the first, to the best of our knowledge, fabrication of LN-on-insulator ridge waveguides with generalized quasiperiodic poled superlattices using the electric field polarization technique and microfabrication techniques. Benefiting from the abundant reciprocal vectors, we observed efficient second-harmonic and cascaded third-harmonic signals in the same device, with normalized conversion efficiency of 1735% W-1 cm-2 and 0.41% W-2 cm-4, respectively. This work opens a new direction for nonlinear integrated photonics based on LN thin film.

On-chip erbium-ytterbium-co-doped lithium niobate microdisk laser with an ultralow threshold.

Erbium-ion-doped lithium niobate (LN) microcavity lasers working in the communication band have attracted extensive attention recently. However, their conversion efficiencies and laser thresholds still have significant room to improve. Here, we prepared microdisk cavities based on erbium-ytterbium-co-doped LN thin film by using ultraviolet lithography, argon ion etching, and a chemical-mechanical polishing process. Benefiting from the erbium-ytterbium co-doping-induced gain coefficient improvement, laser emission with an ultralow threshold (∼1 µW) and high conversion efficiency (1.8 × 10-3%) was observed in the fabricated microdisks under a 980-nm-band optical pump. This study provides an effective reference for improving the performance of LN thin-film lasers.

Coal-mining subsidence changed distribution of the microbiomes and their functional genes in a farmland.

Land subsidence is a serious geological event, and can trigger severe environmental and ecological issues. In this study, the influences of coal-mining subsidence on distribution of farmland microbiomes and their functional genes were investigated by 16 S ribosomal RNA (rRNA) gene and metagenome sequencing. The results showed the existence of a core microbiome, which determined the community compositions across the subsidence farmland. Subsidence decreased the relative abundances of dominant Streptomyces, Nocardioides, and Rhizophagus, but increased the relative abundances of dominant Bradyrhizobium, Rhizobium, and Trichoderma. Subsidence also decreased the relative abundances of genes related to carbon metabolism, Quorum sensing, aminoacyl-transfer RNA (tRNA) biosynthesis, and oxidative phosphorylation, and increased the relative abundances of genes related to two-component system and bacterial chemotaxis. Furthermore, subsidence weakened the biosynthesis of organic carbons by decreasing the relative abundances of genes encoding glycosyl transferases, and strengthened decomposition of degradable organic carbons of the microbiomes and auxiliary activities by increasing the relative abundances of genes encoding glycoside hydrolases and polysaccharide lyases. The concentrations of total phosphorus, Mg2+ , and Ca2+ at the lower areas were significantly higher than those at the upper areas, indicating an associated loss of soil nutrients. Canonical correspondence analysis showed that soil moisture, pH, and the concentrations of NH4 + and Ca2+ were the main factors affecting the distribution of the microbiomes and their functional genes. Collectively, this study shows that coal-mining subsidence alters soil physicochemical properties and distribution of farmland microbiomes and their functional genes.

SAM/SAH Mediates Parental Folate Deficiency-Induced Neural Cell Apoptosis in Neonatal Rat Offspring: The Expression of Bcl-2, Bax, and Caspase-3.

Research demonstrated that folate deficiency in either the mother or father could impact the biological functions of the offspring's of neural cells. Folate deficiency can also impair the methionine cycle, thus contributing to the conversion of S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH), which could potentially cause damage to the central nervous system. The study focused on the effect of parental folate deficiency on neural cell apoptosis in offspring neonatal rats and whether it is mediated by the levels of SAM and SAH in brains. The experimental design was conducted by feeding female and male Sprague Dawley (SD) rats with either folate-deficient or folate-normal diets, sacrificing the offspring within 24 h and isolating their brain tissue. Rats were divided into four groups: the maternal-folate-deficient and paternal-folate-deficient (D-D) group; the maternal-folate-deficient and paternal-folate-normal (D-N) group; the maternal-folate-normal and paternal-folate-deficient (N-D) group; and the maternal-folate-normal and paternal-folate-normal (N-N) group. There was down-regulation of B-cell lymphoma 2 (Bcl-2) expression, up-regulation of Bcl-2-associated X protein (Bax) and Caspase-3 expression of neural cells, and pathological changes in the brain ultrastructure, as well as decreased SAM levels, increased SAH levels, and a decreased SAM/SAH ratio in the rat fetal brain via parental folate deficiency. In conclusion, parental folate deficiency could induce the apoptosis of neural cells in neonatal offspring rats, while biparental folate deficiency had the greatest effect on offspring, and the unilateral effect was greater in mothers than in fathers. This process may be mediated by the levels of SAM and SAH in the rat fetal brain.

Coxiella burnetii Virulent Phase I and Avirulent Phase II Variants Differentially Manipulate Autophagy Pathway in Neutrophils.

Coxiella burnetii is an obligate intracellular Gram-negative bacterium that causes Q fever in humans. The virulent C. burnetii Nine Mile phase I (NMI) strain causes disease in animal models, while the avirulent NM phase II (NMII) strain does not. In this study, we found that NMI infection induces severe splenomegaly and bacterial burden in the spleen in BALB/c mice, while NMII infection does not. A significantly higher number of CD11b+ Ly6G+ neutrophils accumulated in the liver, lung, and spleen of NMI-infected mice than in NMII-infected mice. Thus, neutrophil accumulation correlates with NMI and NMII infection-induced inflammatory responses. In vitro studies also demonstrated that although NMII exhibited a higher infection rate than NMI in mouse bone marrow neutrophils (BMNs), NMI-infected BMNs survived longer than NMII-infected BMNs. These results suggest that the differential interactions of NMI and NMII with neutrophils may be related to their ability to cause disease in animals. To understand the molecular mechanism underlying the differential interactions of NMI and NMII with neutrophils, global transcriptomic gene expressions were compared between NMI- and NMII-infected BMNs by RNA sequencing (RNA-seq) analysis. Interestingly, several genes involved in autophagy-related pathways, particularly membrane trafficking and lipid metabolism, are upregulated in NMII-infected BMNs but downregulated in NMI-infected BMNs. Immunofluorescence and immunoblot analyses indicate that compared to NMI-infected BMNs, vacuoles in NMII-infected-BMNs exhibit increased autophagic flux along with phosphatidylserine translocation in the cell membrane. Similar to neutrophils, NMII activated LC3-mediated autophagy in human macrophages. These findings suggest that the differential manipulation of autophagy of NMI and NMII may relate to their pathogenesis.

Broadband second-harmonic generation in step-chirped periodically poled lithium niobate waveguides.

Periodically poled lithium niobate (PPLN) structures on a chip enable efficient second-order nonlinear optical effects, benefiting from the tight light confinement and the utilization of d33. Here, we report a broadband second-harmonic (SH) generation in a step-chirped PPLN waveguide on X-cut lithium niobate on insulator (LNOI). The high fidelity of the poling period is demonstrated over the whole length of 7 mm using a non-destructive technique of piezoresponse force microscopy. The SH signal was continuously observed in the step-chirped PPLN waveguides while scanning the wavelength of the pump laser from 1550 nm to 1660 nm. The SH conversion efficiency was measured to be 9.6 % W-1 cm-2 at 1642 nm. This work will benefit wavelength conversions of light sources with wideband spectra.

Integrated ytterbium-doped lithium niobate microring lasers.

Integrated and stable microlasers are indispensable building blocks of micro-photonics. Here, we report the realization of an ytterbium-doped lithium niobate microring laser operating in the 1060-nm band under the pump of a 980-nm-band laser. The monolithic laser has a low threshold of 59.32 µW and relatively high output power of 6.44 µW, a state-of-the-art value for rare-earth ions-doped lithium niobate thin-film lasers. The monolithic laser with desirable performance and attractive scalability may find many applications in lithium niobite photonics.

On-chip ytterbium-doped lithium niobate microdisk lasers with high conversion efficiency.

Integrated optical systems based on lithium niobate on insulator (LNOI) have attracted the interest of researchers. Recently, erbium-doped LNOI lasers have been realized. However, the reported lasers have a relatively lower conversion efficiency and only operate in the 1550 nm band. In this paper, we demonstrate an LNOI laser operating in the 1060 nm band based on a high Q factor ytterbium-doped LNOI microdisk cavity. The threshold and the conversion efficiency of the laser are 21.19 µW and 1.36%, respectively. To our knowledge, the conversion efficiency is the highest among the reported rare-earth-doped LNOI lasers. This research extends the operating band of LNOI lasers and shows the potential in realizing high-power LNOI lasers.

Robust and low cost in-fiber acousto-optic Mach-Zehnder interferometer and its application in a dual-wavelength laser.

A robust in-fiber tunable acousto-optic Mach-Zehnder interferometer with a taper-shaped sandwich-like fiber structure is proposed and characterized experimentally, based on which tunable dual-wavelength lasers are demonstrated. The fiber structure was prepared by two-step etching methods, which could be used to fabricate either a symmetric structure for a continuous tuning dual-wavelength laser or an asymmetric structure for a switchable one. The proposed structure has advantages of low cost, low driving power, and robustness. The method for preparing the fiber structure is agile, which paves the way for its applications.

On-chip erbium-doped lithium niobate microring lasers.

Lithium niobate on insulator (LNOI), regarded as an important candidate platform for optical integration due to its excellent nonlinear, electro-optic, and other physical properties, has become a research hotspot. A light source, as an essential component for an integrated optical system, is urgently needed. In this Letter, we reported the realization of 1550 nm band on-chip LNOI microlasers based on erbium-doped LNOI ring cavities with loaded quality factors higher than 1 million at ∼970nm, which were fabricated by using electron beam lithography and inductively coupled plasma reactive ion etching processes. These microlasers demonstrated a low pump threshold of ∼20µW and stable performance under the pump of a 980 nm band continuous laser. Comb-like laser spectra spanning from 1510 to 1580 nm were observed in a high pump power regime, which lays the foundation of the realization of pulsed laser and frequency combs on a rare-earth ion-doped LNOI platform. This Letter effectively promotes the development of on-chip integrated active LNOI devices.

Major Histocompatibility Complex Class II-Restricted, CD4+ T Cell-Dependent and -Independent Mechanisms Are Required for Vaccine-Induced Protective Immunity against Coxiella burnetii.

To understand the role of major histocompatibility complex class I (MHC-I) and MHC-II in vaccine-mediated protection against Coxiella burnetii, we evaluated the protective efficacy of a formalin-inactivated C. burnetii Nine Mile phase I vaccine (PIV) in ß2-microglobulin-deficient (B2m KO) and MHC-II-deficient (MHC-II KO) mice. Vaccination reduced disease severity in wild-type (WT) and B2m KO mice but failed to reduce bacterial burden in MHC-II KO mice. This suggests that the MHC-II antigen presentation pathway is required for PIV-mediated protection against C. burnetii infection. MHC-I and MHC-II affect antibody isotype switching, since both PIV-vaccinated B2m KO and MHC-II KO mice produced less Coxiella-specific IgG than PIV-vaccinated WT mice. Interestingly, MHC-II and CD4 deficiencies were not equivalent in terms of splenomegaly and bacterial clearance. This demonstrates a partial role for CD4+ T cells while revealing MHC-II-restricted, CD4-independent mechanisms. Adoptive transfer of CD4+ T cells from PIV-vaccinated WT mice to naive CD4-deficient (CD4 KO) mice demonstrated that antigen-experienced CD4+ T cells are sufficient to generate protection. Conversely, transfer of naive CD4+ T cells to PIV-vaccinated CD4 KO mice exacerbates disease. Using Tbet-deficient (Tbet KO) mice, we showed a partial role for Th1 subset CD4+ T cells in vaccine protection. Furthermore, Th1-independent roles for Tbet were suggested by significant differences in disease between PIV-vaccinated Tbet KO and CD4 KO mice. Interferon gamma was shown to contribute to the host inflammatory response but not bacterial clearance. Collectively, these findings suggest that vaccine-induced protective immunity against a murine model of experimental Q fever requires MHC-II-restricted, CD4+ T cell-dependent and -independent mechanisms that can be exploited for a new-generation human Q fever vaccine.

Vector beams in planar photonic crystal cavities with rotating air holes.

We report a method to generate angularly polarized vector beams with a topological charge of one by rotating air holes to form two-dimensional photonic crystal (PC) cavities. The mode volume and resonance wavelength of these cavities are tuned from ${0.33}{(\lambda /n)^3}$0.33(λ/n)3 to ${12}{(\lambda /n)^3}$12(λ/n)3 and in a wide range of 400 nm, respectively, by controlling the range of fixed air holes near the center of the structure. As a benefit, the half-maximum divergence angles of the vector beam can be widely changed from 90° to $\sim{60}^\circ $∼60∘. By adjusting the shift direction of the air holes in the PC cavities, optical vector beams with different far-field morphology are obtained. The scheme provides not only an alternative method to generate optical vector beams, but also an effective strategy to control far-field morphology and polarizations, which holds promising applications such as optical microscopy and micro-manipulation.

High-efficiency chirped grating couplers on lithium niobate on insulator.

High-efficiency chirped grating couplers (GCs) with coupling efficiencies (CE) approaching 90%/coupler were designed by using a particle swarm optimization algorithm. These GCs were fabricated on $z$-cut lithium niobate on insulator (LNOI) with an Au layer on the lithium niobate substrate. The maximum CEs for transverse electric and transverse magnetic polarization input were measured up to ${\sim}{72.0}\%$/coupler and ${\sim}{61.6}\%$/coupler, respectively, which are the state-of-the-art values for LNOI GCs as far as we know. These GCs contribute to the realization of high-efficiency LNOI on-chip integrated optics.

Dual-periodically poled lithium niobate microcavities supporting multiple coupled parametric processes.

Periodically poled lithium niobate (PPLN) microcavities with additional reciprocal vectors attract attention as a platform for efficient parametric nonlinear optical processes with wavelength and polarization flexibility. Here, we report the simultaneous realization of multiple coupled parametric processes in PPLN microdisk cavities with dual periods as a result of the significantly increased number of reciprocal vectors to fulfill quasi-phase matchings for a series of nonlinear processes. PPLN microdisks with up to 1.43×105 quality factors and unit domain size of 90 nm in width were fabricated using CMOS compatible microfabrication techniques and electrically poled with the help of piezoresponse force microscopy. The conversion efficiency of second-harmonic signal was measured to be 51%W-1. Our work paves the way towards efficient cascaded parametric effects including third- and fourth-harmonic generations.

A three-dimensional self-standing Mo2C/nitrogen-doped graphene aerogel: Enhancement hydrogen production from landfill leachate wastewater in MFCs-AEC coupled system.

A hydrothermal-annealing method was adopted to form nitrogen-doped graphene aerogel-supported molybdenum carbide (Mo2C/NGA) materials by using graphene oxide (GO), poly (propylene glycol) bis(2-aminopropyl ether) (D400 for short) and ammonium molybdate as precursors. The annealing temperature and GO/D400 wt ratio played an important role on the materials structure and electrocatalytic activity. When the annealing temperature reached to 800 °C, the Mo2C was formed as an active component and improved obviously the hydrogen evolution reaction (HER) activity. After introducing the appropriate amount of D400, the Mo2C/NGA material not only had a firm porous monolithic framework, but also presented an increasing HER activity. Further, the Mo2C/NGA-based microbial fuel cells-ammonia electrolysis cell (MFCs-AEC) coupled system was constructed and operated for higher hydrogen production. The coupled system produced hydrogen of 198 mL g-1Mo2C/NGA in simulated ammonia-rich wastewater. As using the actual landfill leachate wastewater as substrate, there was 79.2 mL g-1Mo2C/NGA of hydrogen production. All of these were attributed to the porous structure with an interconnected network and the nitrogen-doped structure of the NGA.

Discrimination of five brands of instant vermicelli seasonings by HS-SPME/GC-MS and electronic nose.

The flavor profile of five brands of instant vermicelli seasonings were identified by headspace solid-phase micro-extraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS) and electronic nose (e-nose). GC-MS showed that the volatile compounds of instant vermicelli seasonings were significantly different. Alkenes, alcohols, aldehydes and ketones were the major volatile compounds in instant vermicelli seasonings. The seasonings could be classified based on differences in volatile compounds. The overall volatiles profiles were also analyzed by e-nose. E-nose determination and GC-MS statistical analysis had similar results. The volatile compounds showed good correlation with e-nose sensors according to partial least square regression models. Both methods had good potential application in evaluating flavor quality and differentiating among instant vermicelli seasonings.